1. Field of the Invention
The present invention relates to a method for transmitting additional information, particularly specifics concerning date and time of day, in conjunction with message signals which are transmitted over a data switching center belonging to a public switched network and to which teleprinter subscriber stations are connected. The teleprinter subscriber stations are capable of transmitting and receiving message signals with a first transmission procedure. The data switching center is also connected to teletex subscriber stations which are capable of transmitting or receiving message signals with a second transmission procedure differing from the first transmission procedure. The transmission of message signals between teleprinter subscriber stations and teletex subscriber stations occurs over at least one signal converter which is also connected to the data switching center and which takes a conversion of the message signal supplied thereto with the first or second transmission procedure into message signals to be forwarded with the second or, respectively, first transmission procedure.
2. Description of the Prior Art
A circuit arrangement for the transmission of message signals between subscriber stations operating according to a first transmission procedure and subscriber stations operating in accordance with a second transmission procedure which differs from the first transmission procedure over a data switching center is already known in the art, for example from the U.S. Pat. No. 4,323,728, which is fully incorporated herein by this reference, and must be referred to as a signal converter. Given this known circuit arrangement, a plurality of converter devices is provided which is connected to termination circuits of a data switching center, the plurality belonging to two different groups of termination circuits. Such a converter is employed for the execution of the required conversion operations in the course of a connection between a subscriber station operating with the first transmission procedure and a subscriber station operating with the second transmission procedure.
It is provided in various known transmission procedures, for example in the teletex procedure, that, given an existing connection, indication of date and time of day are placed in front of the message signals to be transmitted, this being provided as additional information by the teletex subscriber stations. Given connections of telex subscriber stations to teletex subscriber stations, however, it has not heretofore been possible to transmit such additional information as required together with the message signals to be transmitted.